Fuel economy is an important feature in engine, fuel and lubricant development. By lowering the friction of the engine, less of the power put into it is lost and more energy is spent on moving the vehicle. Consequently, a vehicle can run for a longer time on the same amount of fuel.
Motor oil is used for the lubrication, cooling, and cleaning of internal combustion engines. Thus, its main function is to help surfaces slide relative to each other preventing wear to the engine. Most motor oils are derived from crude oil, with additives to improve certain properties. The bulk of motor oil typically consists of hydrocarbons with between 18 and 34 carbon atoms. One of the most important properties of motor oil in maintaining a lubricating film between moving parts is its viscosity, which must be high enough to maintain a lubricating film, but low enough that the oil can flow freely to reach the engine parts under all conditions that would most likely be encountered. An important parameter in this connection is the viscosity index, which is a measure of how much the viscosity of the oil changes due to temperature. A higher viscosity index indicates that the viscosity changes less with temperature than a lower viscosity index.
At slow enough speed of the moving parts or low enough viscosity surface asperities come into contact. At this stage the surfaces will only be protected by a very thin film on each surface. One of the additives making this film is the anti-wear additive zinc dialkyl dithiophosphate, ZDDP. ZDDP prevents wear of the metal surfaces by reacting with metal oxides on the metal surface to create a protective metal sulphide film (for most engines the film is iron sulfide). This soft sulphide film protects engine parts by sacrificing itself in lieu of wearing the harder metal surface.
Another type of additives is friction modifiers, which go to the surface to create a film. A common friction modifier is the inorganic molybdenum dithiocarbamate. This friction modifier works by breaking down on the surface to form a layer of molybdenum disulphide sheets. These sheets consist of a plate-like structure containing layers of molybdenum atoms sandwiched between layers of sulphur atoms. Between each adjacent layer of sulphur atoms are weak bonds that allow each plate to slide easily over one another resulting in a low coefficient of friction.
U.S. Pat. No. 4,314,907 relates to oil additive compositions for internal combustion engines containing at least one dithiophosphate, at least one fatty amide and a fluorographite CFx, where x is between 0.6 and 1 and oils containing such compositions. The fatty amide could e.g. be prepared by reaction between alkylene diamines and fatty acid.
U.S. Pat. No. 5,174,914 relates to an aqueous liquid lubricant composition for a chain driven conveyor system, which composition includes fatty acid diamine salts, a hydrotrope for providing sufficient aqueous solubility, an anionic or nonionic surfactant, and a chelating agent.
U.S. Pat. No. 5,549,838 relates to hydraulic working oil compositions for use in buffers comprising a phosphoric acid ester, and/or a phosphorous acid ester, and at least one kind of a nitrogen-containing compound selected from the group consisting of an alkylene oxide adduct of an aliphatic monoamine, an aliphatic polyamine, a salt of the polyamine with an aliphatic acid having 6-22 carbon atoms, and an aliphatic monoamine. The salt is preferably one in which one aliphatic acid per nitrogen atom in the aliphatic polyamine has been reacted with the aliphatic polyamine, to form a salt such as octyl ethylenediamine-dimyristate.
US 2009/0005278 A1 relates to a lubricating oil composition for internal combustion engines comprising a base oil having a lubricating viscosity and additives composed of a) a salt of an alkali metal or alkaline earth metal and an alkylsalicylate and/or alkylcarboxylate, b) a nitrogen atom-containing ashless dispersant and/or a nitrogen atom-containing dispersive viscosity index improver, c) a neutral salt of a fatty acid and a fatty amine, and d) an oxidation inhibitor, which composition is effective for lubricating diesel engines using a low sulfur-content fuel. Preferred compounds c) are exemplified by salts of oleic acid with different fatty monoamines and by a salt of 2 moles oleic acid with one mole N-oleylpropylenediamine.
U.S. Pat. No. 4,581,039 relates to certain hydrocarbyl hydrocarbylenediamine carboxylates, which can be made by the reaction between an appropriate diamine and an organic monocarboxylic acid, and to lubricant and fuel compositions containing the same. The products may be formed from one diamine and one monocarboxylic acid, or from one diamine and two monocarboxylic acids.
However, there is still a need for more effective lubricating oil compositions.